The present invention relates to motion-picture cameras utilizing a reflex shutter mechanism (usually a rotating shutter) which alternates between an exposure phase and a reflex phase. During the reflex phase, the shutter reflects scene light onto a light-sensitive means which furnishes a light-indicating signal. This signal is then used as a feedback signal for application to a negative-feedback diaphragm control arrangement.
With motion-picture cameras of the type in question, deviations of the shutter-motor speed from the rated speed value can cause improper exposure. If the shutter-motor speed is below rated speed, each exposure phase will be longer than the rated value. However, inasmuch as the light-indicating signal furnished to the negative-feedback diaphragm control arrangement is not dependent upon the duration of the exposure and reflex phases, the lengthened exposure phase is not taken into account in the automatic selection of the diaphragm setting. Thus, apart from undesirable effects resulting from the lowered shutter speed per se, there will be the additional problem that the exposed frames will tend to be overexposed. An analogous difficulty arises when the speed of the motor driving the shutter is above the rated value.